CN112334227A - Nanoparticles and method of preparation - Google Patents

Abstract

The present invention relates to a composite material comprising supported nanoclusters comprising one or more metal ion containing compounds, wherein each metal ion containing compound is a transition metal complex having ligands coordinated to a transition metal ion selected from the group consisting of: glyoxime; glyoxime derivatives; salicylaldimine; and salicylaldimine derivatives; and wherein the nanoclusters are spaced apart across one or more surfaces of the carrier; a material prepared from the composite material by annealing; and solution-based methods for forming the composites and materials. The use of these metal ion-containing compounds, i.e. the use of the products as catalysts and adsorbents, is also described.

Description

Nanoparticles and method of preparation

Technical Field

The present invention relates to a method for preparing metal nanoparticles. In particular, but not exclusively, the invention relates to nanoparticles, especially supported nanoparticles, and composite materials prepared during the formation of these nanoparticles. These nanoparticles are suitable for use as a material active towards gases, such as a catalytic material or an adsorbent material. The invention also relates to a material comprising nanoparticles.

Background

Catalysts are almost ubiquitous: they are used in an ever-increasing range of processes and for a wide variety of applications. Thus, there is a general and continuing drive to find new and improved catalysts and methods for their preparation.

Many catalysts and other active materials are used in conjunction with gas phase reactants, but the active materials themselves are typically solids. One group of applications where active materials are particularly desirable is the treatment of exhaust gases from fuel engines. Current fuel engines such as diesel engines obviously inevitably produce several undesirable gases as a by-product of the combustion process. Currently, active materials are used in a variety of applications, including for diesel and Compressed Natural Gas (CNG) oxidation, lean and stoichiometric NOx reduction, gasoline three-way catalysis, methane oxidation (MeOx), ammonia oxidation, and passive NO_xAdsorbent (PNA). Thus, an exhaust system for an engine may have several different materials, for example, present as part of a separate device tailored for a particular function.

Most generally, materials for such applications (including MeOx and PNA) typically comprise transition metal nanoparticles distributed on a support material. The transition metal nanoparticles used vary in composition depending on the application. Generally, they are nanoparticles based on: a single metal, an intimate mixture of metals, an alloy, or an oxide of any single metal, intimate mixture, or alloy.

In general, it is preferred that the nanoparticles be uniform in size and have a good, uniform distribution over the surface of the support to maximize efficiency. In some cases, it is desirable to control the location of the deposition of the transition metal nanoparticles. It is also desirable to have small particles to maximize the available surface area for catalyzing the appropriate reaction or adsorption. Thus, in general, it is desirable to be able to control the size, location and/or distribution of the nanoparticles on the surface of the support.

Another challenge, particularly with materials used to treat exhaust gas, relates to the fact that the temperature of the exhaust gas is relatively low (e.g., about 400 c for diesel engines, for example). Therefore, it is desirable to develop catalysts and PNAs and other active materials that function well and are durable at these temperatures.

The activity of an oxidation catalyst is typically measured in terms of its "light-off" temperature. This is the temperature at which the catalyst starts to function, or the temperature at which the catalyst functions at a certain level. The temperature can be given in terms of the level of conversion of the reactants. Different catalysts typically have different "light-off temperatures, but as noted, the useful upper limit is typically quite low for exhaust systems. The performance of such catalysts is important, for example, because it affects the performance of any downstream emission control device.

Another challenge relates to the formation of nanoparticles comprising multiple metal elements (multiple metals). In general, it is desirable to have small particles to maximize the available active surface area. For example, the formation of metal alloys typically requires heating at high temperatures to thoroughly mix the different types of metal atoms. Unless the spacing is large, individual nanoparticles will typically agglomerate during this heating step. Thus, the metal alloy particles may grow to a size that results in lower efficiency.

Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art. In particular, in preferred embodiments, the present invention seeks to provide improved metal nanoparticles and metal nanoparticle-containing composites and materials for use as active materials, particularly for applications such as MeOx and PNA, as well as improved and varied methods for preparing metal nanoparticles.

Disclosure of Invention

According to a first aspect of the present invention there is provided a composite material comprising supported nanoclusters, said nanoclusters comprising one or more metal ion-containing compounds,

wherein each metal ion-containing compound is a transition metal complex having a ligand coordinated to the transition metal ion, the ligand being selected from the group consisting of: glyoxime; glyoxime derivatives; salicylaldimine; and salicylaldimine derivatives; and wherein the nanoclusters are spaced apart across one or more surfaces of the carrier.

According to a second aspect of the present invention there is provided a material formed from the composite material of the first aspect, wherein the composite material is subjected to a heating step to form metal-containing nanoparticles from the nanoclusters.

According to a third aspect of the present invention there is provided a catalyst or passive NO comprising the material of the second aspect_xAn adsorbent.

According to a fourth aspect of the present invention there is provided a method of forming supported metal-containing nanoparticles or oxides thereof, the method comprising:

a. providing one or more transition metal ions by providing one or more metal ion-containing compounds, and providing a support;

b. dissolving the one or more metal ion-containing compounds in a solvent;

c. a step of mixing the carrier with the dissolved one or more metal ion-containing compounds;

d. a heating step wherein the one or more metal ion-containing compounds are subjected to a temperature of at least 300 ℃ to form metal-containing nanoparticles or oxides thereof on the support;

e. a cooling step comprising cooling the product of step d; and optionally

f. Acid leaching;

wherein the one or more metal ion-containing compounds is a transition metal complex having a ligand coordinated to a transition metal ion, the ligand selected from the group consisting of: glyoxime; glyoxime derivatives; salicylaldimine; and salicylaldimine derivatives.

The method of the fourth aspect comprises providing a support such that the nanoparticles comprising one or more metals or oxides thereof are formed on the support. Such supported nanoparticles are advantageous in processing and downstream applications. More preferably, the heating step of these aspects is carried out in an oxidizing atmosphere. The methods herein allow for the use of comparable temperatures during manufacturing, such as between 300 ℃ and 600 ℃, which is advantageous from an environmental and manufacturing perspective. The oxidizing atmosphere also substantially avoids or minimizes the formation of a coating on the surface of the nanoparticles during manufacture, which may be desirable for certain applications described herein.

Preferably, the method produces a material according to the second aspect.

According to a further aspect of the present invention there is provided the use of at least two metal ion containing compounds selected from the group consisting of metal glyoxime, a metal glyoxime derivative, a metal salicylaldimine and a metal salicylaldimine derivative in a method of forming metal nanoparticles or an oxide thereof, the metal nanoparticles comprising at least two transition metals; use of a metal ion-containing compound in a method of forming metal-containing nanoparticles or oxides thereof, the metal ion-containing compound being a metal glyoxime, a metal glyoxime derivative, a metal salicylaldimine or a metal salicylaldimine derivative, the method comprising dissolving the metal ion-containing compound in a solvent; optionally forming the composite of the first aspect or the material of the second aspect, or wherein the method is a method according to the third aspect; and metal-containing nanoparticles or oxides thereof as catalysts or in passive NO_xUse in an adsorbent.

It will be appreciated that features described with respect to one aspect of the invention may be equally applicable to another aspect of the invention. For example, features described with respect to the first aspect of the invention may equally be applicable to the second, third and/or other aspects of the invention, and vice versa. Some features may not be applicable to and may be excluded from particular aspects of the invention, but this will be apparent from the context.

Drawings

Embodiments of the present invention will now be described, by way of example and not in any limitative way, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic representation of supported metal alloy nanoparticles prepared according to the method of the present invention.

FIG. 2a is a schematic diagram showing the theoretical results of combining two metal glyoximes, wherein different first and second metal centers are each bound by M¹And M²And (4) showing. Each M independently represents a metal as defined herein; each R independently represents H or a derivative group as described herein. M¹And M²The relative order of and orientation of the ligands is used for exemplary purposes. The present invention is not limited to this orientation or sequence, but encompasses any orientation or sequence within the limitations described herein.

FIG. 2b is a schematic diagram showing the theoretical results of combining three metal glyoximes, wherein a first metal center, a second metal center and a third metal center, which are different from each other, are formed by M¹、M²And M³And (4) showing. Each of M and R has the same definition as in fig. 2 a. M¹、M²And M³The relative order of and orientation of the ligands is used for exemplary purposes. The present invention is not limited to this orientation or sequence, but encompasses any orientation or sequence within the limitations described herein.

Fig. 3 is a Transmission Electron Microscope (TEM) image (a) and a particle size distribution (b) of Pd-and Pt-containing nanoparticles prepared by the deposition precipitation method according to example 1. The scale bar in fig. 3a is 20 nm. Fig. 3b shows the average particle size 4.7 nm; δ 1.3 nm.

Figure 4 is a TEM image of Pd and Pt containing nanoparticles prepared by the deposition precipitation method according to example 4 before firing (a) and after firing in air at 500 ℃. The scale bar in each image is 30 nm.

Fig. 5 relates to PtPd nanoparticles prepared by a deposition precipitation method according to example 5. Figure 5a shows a TEM image of a sample prepared by annealing at 500 ℃ in air and represents a "fresh" sample; figure 5b shows a TEM image of the sample after exposure to 700 ℃ for 40 hours after the initial annealing process and represents an "aged" sample. FIG. 5a is a scale bar of 50 nm; the scale bar of fig. 5b is 100 nm.

Figure 6 shows the results of methane oxidation tests using 3Pd/ZSM-5 (i.e., Pd on a ZSM-5 zeolite framework support) prepared by a precipitation method as described herein. FIG. 6a shows in the absence of SO₂Water resistance in the case of (a); and FIG. 6b represents SO₂The effect on the activity. In each figure, the solid grey line (mainly lower than the black line) represents the methane conversion performed by the sample prepared using PdN; the solid black line (mainly above the grey line) represents the sample according to the invention. The dotted line represents temperature; the peak temperature was 550 ℃ and the temperature at the end of the test was 400 ℃. In fig. 6a, the water content in the feed is about 10%. In FIG. 6b, the sample is exposed to 2ppm SO₂100 minutes, and SO₂The remaining 80 minutes were shut off. In SO₂During the shutdown period the temperature was again raised to 550 ℃ and then lowered to 440 ℃.

FIG. 7 compares the use of Pd-DMG with (a, b)₂A method of precipitation as a component containing metal ions and (c, d) particle size and dispersibility of 3Pd on zeolite prepared by a corresponding method using palladium nitrate. Fig. a and c are representative high resolution TEM images, each with a scale bar of 50 nm. The corresponding particle size distributions are shown in fig. b and d, i.e. particle size distribution b corresponds to sample a (average size 7.2 nm; δ 3.6) and particle size distribution d corresponds to sample c (average size 12.6; δ 6.9).

FIG. 8 shows the use of Pd-DMG₂Deposition precipitation prepared zeolite (having the same pattern as that of figure)TEM images of 3% Pd on different silica to alumina ratios (SAR)) used in the samples. Fig. 8a shows the particles before annealing (about 2nm size) and after annealing at 500 c for 2 hours (about 5-7nm size). The scale bar is 20nm in fig. 8a and 50nm in fig. 8 b.

FIG. 9 shows NO of example 10 and comparative example 6_xStorage performance.

Detailed Description

The present invention has several advantages, including but not limited to:

providing a material having metal-containing nanoparticles of controlled size and composition, and having relatively high uniformity and distribution throughout the support, in turn having improved properties;

there is provided a single vessel process or one pot process for the preparation of single-clock metal nanoparticles, metal alloy nanoparticles, nanoparticles comprising an intimate mixture of metals or their oxides, said nanoparticles having a size, uniformity and distribution throughout the support useful for a variety of catalytic and related applications;

the method avoids significant growth of nanoparticles (particularly metal alloy nanoparticles);

and

the inventors believe that this results in more stable supported metal-containing nanoparticles suitable for use as active materials, such as catalysts and adsorbents.

On a general level, the present invention provides metal nanoparticles, particularly supported metal nanoparticles and particularly supported transition metal nanoparticles. It is believed that there are a variety of nanoparticles that can be provided according to the present invention. It is contemplated that the flexibility of the present invention makes it possible to apply the present disclosure to a range of types of supports and a range of catalysts and related materials, such as adsorbents.

For example, the present invention provides single-metal and multi-metal nanoparticles, and oxides of each of the single-metal and multi-metal nanoparticles. The general terms "metal nanoparticles" or "metal-containing nanoparticles" as used herein include each of these options. The term "multi-metallic nanoparticles" encompasses nanoparticles comprising an intimate mixture of metals as well as metal alloy nanoparticles, and is not particularly limited by many different types of metals (although two are generally the most common). Reference to "an oxide thereof" refers to an oxide of a metal and refers to each of the types of components listed which contain a single metal or multiple metals.

Definition and interpretation

As used herein, the expression "C_x-y"(wherein x and y are integers) is used in the normal sense, i.e., it means having between x and y carbon atoms in the chain.

The term "square planar surface" is well known in the art. Generally, it refers to a coordination compound or complex having coordinating ligand atoms located at approximately square corners around the center of the transition metal ion.

The skilled person realizes that some deviations from exact planarity and exact square shape are encompassed within the meaning of square planar as used in the art and herein.

The prefix "nanometer" is commonly used in the art to describe dimensions measured on the nanometer scale. In the context of the present specification, "nano" refers to a dimension between 0.5nm and 100 nm. This may include reference to prior art or comparative dimensions; specific definitions of, for example, size ranges suitable for use in the products of the invention are listed elsewhere.

As used herein, the term "passivation" has the meaning understood by the skilled person, i.e. a treatment that renders the metal surface inert (non-reactive). It is well known that this typically occurs by forming a film or coating of metal oxide on the metal surface.

The term "acid leaching" herein has the meaning understood by the skilled person, i.e. treatment of the metal with acid to extract the acid soluble components.

The term "nanoclusters" is used to describe the agglomeration or accumulation of molecules having nanometer dimensions as defined elsewhere herein. The term encompasses, but is not necessarily limited to, random or ordered arrangements of molecules, such as stacks or chains. No limitation on the shape is intended.

Zeolites and zeotypes (sometimes referred to as molecular sieves) are crystalline microporous solids having an ordered microporous structure. They are defined not only by their composition, but also by the arrangement of tetrahedral atoms which combine to form the cavities, channels and/or pores of the structure. A complete list of framework types is maintained by IZA (international zeolite association) at http:// www.iza-structure.org/data-bases/and each framework type is assigned a unique 3-letter code. Zeolites have traditionally been considered TO be built up of repeating TO₄Crystalline or quasi-crystalline aluminosilicates of tetrahedral units, where T is typically Al and Si (although other atoms such as B, Fe and Ga have been described). For aluminum phosphate, T is Al and P. Zeolites are typically doped with other ions to induce ion exchange properties, or with charge equivalent ions to give different types of sites.

By the term "zeolite-based" we mean doped zeolites. As non-limiting examples, the zeolite may be doped with one or more elements, such as Cu, P, or Na. As used herein, "zeolite" encompasses "zeolite-based" unless explicitly stated otherwise.

The term "NOx" in the context of the present invention is well known to the skilled person. It refers to nitrogen oxides. In particular, it relates to nitrogen oxides produced by internal combustion engines and emitted as exhaust gases.

The term "intimate mixture" refers to a mixture that is pseudo-homogeneous on a nanometer scale.

As used herein, the term alloy has the standard meaning understood by those skilled in the art and encompasses materials having metal-metal bonds between alloying elements.

Diesel oxidation, as described in the background section, is a term of art that encompasses the oxidation of CO, hydrocarbons, and NO in fuels. Similarly, gas triple oxidation is a recognized term of art and encompasses substantially consistent oxidation of CO and hydrocarbons as well as NOx reduction.

By "slurry" is meant a liquid that contains insoluble materials, such as insoluble particles.

When the specification refers to "a" or "an", this covers both the singular and the plural.

Product(s)

Metal-containing nanoparticles according to the present invention are nanoparticles comprising a single metal, multiple metals or oxides of each of these metals. The metal is a transition metal.

In case the metal comprises more than one metal, the metal nanoparticles comprise at least two metals, in particular at least two transition metals. The transition metal is an element of group 3 to group 12 of the periodic table. Different metallic elements are sometimes referred to herein as different types of metals. Preferred transition metals are listed elsewhere herein.

The at least two transition metals may optionally be alloyed together. Preferably, the alloy nanoparticles are bimetallic alloy nanoparticles, but they may alternatively be trimetallic or higher order alloy nanoparticles. Alternatively, the at least two transition metals may not be alloyed together in a metallurgical sense, but may be a mixture of metals.

It should be understood that the use of an inert atmosphere is unlikely to produce the oxides of the various metal-containing nanoparticles described herein. In an oxidizing atmosphere, at least some oxidation, such as partial oxidation, may occur, for example, at the surface of the nanoparticle, or oxidation may occur throughout the nanoparticle. As used herein, oxides can encompass mixed oxides, as well as mixtures of oxides. The skilled artisan knows that certain metals (e.g., Pt and Au) are generally difficult to oxidize, and in such cases, other oxidation methods known to the skilled artisan may be required to obtain the metal oxide, if desired.

The nanoparticles of the present invention are typically fine particles of one or more metals. Their size is typically less than 50nm and more typically less than 20 nm. Preferably, the nanoparticles of the present invention have an average size of about 15nm or less. The lower size limit of the nanoparticles is not particularly limited, but they may be as small as, for example, 0.5nm, and usually at least 1 nm. The average size range of the alloy nanoparticles prepared herein is typically between 1nm and 50 nm. Particularly preferred average sizes for the presently described applications are at most 10nm, at most 9nm or at most 8 nm. Of particular interest are average sizes between 2nm and 7nm, such as 3nm or 4 nm.

The size of a particle refers to the width of the particle, which is the diameter of a spherical or spheroidal particle. Methods of measuring particle size are known to the skilled person and may include, for example, analyzing TEM images.

The shape of the prepared metal-containing nanoparticles is generally spheroidal, but the invention is not limited to this shape. The metal nanoparticles may have any convenient shape, including but not limited to ellipsoidal, acicular, and spherical (spheroidal).

In the case where the metal-containing nanoparticles comprise more than one metal, the skilled person can select the appropriate ratio of each metal as desired. The amount of each metal in the nanoparticles is not particularly limited. By way of example, the metal to metal weight ratio may be between about 99:1 to 1:99, such as between 80:1 to 1:80 or 60:1 to 1: 60. In some embodiments, particularly but not exclusively in particularly preferred embodiments using Pd and Pt, the metal to metal weight ratio may be between about 25:1 to 1:25, such as 10:1 to 1:10 or 3:1 to 1:3, including, 1: 1.

The metal-containing nanoparticles can be used at the end of the cooling step or after the optional leaching step (if appropriate) in the form of metal-containing nanoparticles. Alternatively, the metal-containing nanoparticles may be further treated prior to use. Exemplary additional steps are discussed elsewhere herein.

Without being bound by theory, the inventors believe that certain metal nanoparticle preparation methods, particularly in an inert annealing atmosphere, produce nanoparticles having a coating (also referred to herein as an "overlayer") that generally extends substantially continuously over the product. X-ray photoelectron spectroscopy (XPS) data has been used to indirectly infer its presence. In particular, XPS data indicates that the coating contains nitrogen, oxygen, and carbon. It is believed that this coating, formed particularly during the manufacture of metal alloy nanoparticles under inert conditions, helps to prevent agglomeration or sintering of the nanoparticles. Agglomeration and sintering are often found to be particularly problematic during the heating required to form the metal alloy.

This result is unexpected. US 2010/152041 a1 discloses a method for the preparation of monometallic nanoparticles, which method comprises heating a powder comprising two dimethylglyoxime molecules and a chelate complex of a transition metal, optionally in the presence of alumina, at 300-400 ℃ to form Ni nanoparticles. The preparation methods described herein involve heating the Ni-DMG powder directly in air, or milling the Ni-DMG powder with alumina whiskers and then heating. This document reports that Ni nanoparticles are formed on carbon particles in the absence of alumina, and supported on alumina in the presence of alumina. It is also described that at temperatures above 400 ℃, significant sintering and/or agglomeration is observed, i.e. significantly larger particles are produced. Thus, the present invention is more applicable than previously known methods, at least because higher temperatures can be used with minimal sintering and/or agglomeration. There is no suggestion that a coating can be formed. Unpredictably, solution-based metal nanoparticle preparation as described herein may also yield excellent results.

FIG. 1 is a schematic representation of a product prepared according to the process of the present invention. In fig. 1, the carrier is shown in black at the bottom of the figure. This may be any suitable carrier as described herein. In fig. 1, the carrier is shown as having a flat lower surface and an irregular upper surface, but this is not limiting in the present invention.

The grey hexagons represent metal-containing nanoparticles. The hexagonal shape is not limiting. In addition, although these hexagons are shown in fig. 1 as being of the same size, this does not of course necessarily represent all products produced according to the process of the invention, i.e. they may have different sizes from one another. The metal-containing nanoparticles in fig. 1 are divided into spheres representing various metal elements. Like the hexagonal shape, the spherical shape is not representative of the individual domains of metal within the nanoparticle, as they can, of course, take on a variety of shapes and sizes. It should be noted that each sphere may represent any suitable number and type of metals, as well as any suitable bonding such as alloying particles.

The composite material of the present invention typically comprises a support material and nanoclusters of molecules, which are metal ion containing compounds as defined elsewhere. In practice, the support will comprise a plurality of nanoclusters. The nanoclusters are typically dispersed or distributed on one or more surfaces of the support. That is, they are spaced apart (i.e., arranged with no nanocluster regions separating them) so that individual nanoclusters may be identified. It has been found that nanoclusters show good distribution throughout the support; that is, they do not clump together or agglomerate. See, for example, fig. 4 a. In fig. 4a, a small spheroidal region in light gray can be seen, separated by regions in dark gray or black. The light grey areas are nanoclusters, especially metal ions of the compound containing cluster metal ions. It can be seen that the nanoclusters of this example are relatively uniform in size, well separated from each other and have a good distribution throughout the support. Similar properties can be seen for light grey nanoparticles formed from these nanoclusters, see e.g. fig. 4b, where the very light spheroidal regions are nanoparticles and are also separated by lighter grey regions.

Depending on the type of carrier used, the location and/or distribution of the nanoclusters may be controlled. For example, materials having ion exchange sites are suitable for controlling the location and/or distribution of nanoclusters of the composite material and may be used in the method of the present invention.

Without being bound by theory, it is believed that nanoclusters include a stack of metal ion-containing compounds having aligned chains of metal ions. This ability to form a stack is believed to result in intimate metal-metal interaction, intimate mixing (stacking) of metal ions, and rapid precipitation during fabrication. Thus, the diffusion distance is small and therefore the metal ions need only a small movement when heated to form metal-containing nanoparticles, in particular metal alloy-containing nanoparticles.

The composite material of the present invention is an intermediate formed during the process of the present invention after deposition and precipitation of the metal ion containing compound on the support, but before the heating step for separating, partially separating, decomposing or substantially decomposing the ligand from the metal ion of the metal ion containing compound. Although an intermediate, the composite material can be isolated and evaluated. The composite material may be annealed/heated/fired to provide transition metal-containing nanoparticles. The heating step is sometimes referred to herein as annealing or firing. That is, the ligand of the metal ion-containing compound (complex) is partially, substantially or completely removed or separated from the metal ion, and the metal ion itself forms a metal-metal bond. In some cases, complete removal and optional decomposition of the ligand is contemplated. The resulting materials (sometimes referred to as "active" materials) can be used in catalytic or related applications. It is noted that the composite material comprising nanoclusters may also be active, e.g. as a catalyst or adsorption material; this possibility is not intended to be excluded.

The nanoclusters may show a slightly smaller size than the final nanoparticles (as seen by comparing e.g. fig. 4a and 4 b) or they may be substantially similar or even larger in size (the nanoclusters may e.g. shrink as the ligands decompose during the firing step). Nanoparticle and nanocluster sizes can be measured by TEM or XRD according to known and standard methods and protocols. For example, TEM images may be taken and appropriate software used to determine the nanoparticle or nanocluster size. Alternatively, TEM images can be printed and measured by hand.

Thus, the average size of the nanoclusters may be less than 50nm, typically less than 30nm and less than 15 nm. The nanoclusters may have an average size greater than 0.5nm, typically greater than 1nm, and in some cases greater than 1.5 nm. Preferably, the average size of the nanoclusters ranges between about 0.5nm and 10nm, typically between 1nm and 7nm, and preferably between 1.5nm and 5nm, such as 2nm or 3 nm.

The metal-containing nanoparticles can be used as part of a catalytic material, particularly as part of a catalyst for oxidation reactions (such as MeOx). Metal-containing nanoparticles may alternatively be used as part of different types of active materials, such as adsorbent materials used in PNAs, for example.

For such applications, the supported nanoparticles prepared by the methods described herein may be provided as a powder. These powders are typically applied to structures such as ceramic or metal honeycomb structures. The nanoparticle-containing powder may optionally be dispersed in water, for example to prepare an aqueous slurry, to provide a form suitable for coating. The slurry or dispersion may be formulated with organic and/or inorganic additives according to the necessity or preference for compatibility with the particular coating process contemplated.

In some alternative examples, nanocluster deposition may occur within the coating slurry by adding a solubilizing solution of the metal-containing compound to the dispersed support and adjusting the pH to ensure that the nanoclusters are deposited on the support, as described elsewhere herein. The resulting metallization slurry can then be formulated for coating and then applied to a suitable structure by adding the additives described above. Generally, the coating is then annealed to stabilize the adhesion and cohesion of the coating, and in this case, the nanoclusters decompose to form metal-containing nanoparticles.

The catalytic materials and other active materials of the present invention are prepared from the composite materials described herein. Generally, active materials are prepared by converting nanoclusters of metal ion-containing compounds to metal-containing nanoparticles. This is typically achieved by annealing as described above. It is believed that the annealing process decomposes the metal ion-containing compound, thereby removing or substantially removing the ligand of the metal ion-containing compound. This in turn allows the metal ions to bond with the metal-containing nanoparticles to form from the nanoclusters.

Thus, if the nanoclusters comprise a metal ion containing compound having one metal ion, the annealing process provides a catalytic material having a single metal nanoparticle. If the nanoclusters include more than one metal ion in the metal ion-containing compound, the annealing process provides the catalytic material with multi-metallic nanoparticles.

The use of oxidation conditions during annealing may promote oxidation of the metal present in the nanoclusters and form metal oxide-containing nanoparticles. This in turn is believed to result in the formation of metal oxide-containing nanoparticles. For example, the use of air during annealing can produce metal oxide-containing nanoparticles. The composite material is preferably annealed under oxidizing conditions, most preferably under air. The skilled person understands that in some instances where the metal is more stable, such as Pt or Au, oxidation may be more difficult, particularly at higher temperatures, and thus the metal, rather than its oxide, may result from the use of an oxidizing atmosphere.

More details of preferred annealing conditions are described below under the heading "heating step".

The skilled person will determine the loading of metal on the support according to the desired application. In general, however, it is contemplated that metal loadings of up to 10 wt%, such as about 9.5 wt% or less, will be advantageous. Suitable metal loadings are at least 0.5 wt%, such as 1 wt% or more. A suitable range of metal loading may be between 1 wt% to 7 wt%, preferably between 2 wt% to 6 wt%. Too high a metal loading can result in unacceptably large metal particle sizes.

It has been found (see also experimental section) that the catalyst prepared according to the process of the invention has improved properties. For example, the catalyst of the present invention is less SO-depleted than catalysts prepared by other methods₂And (4) inactivating. Without being bound by theory, it is believed that this is due to SO₂Rapid oxidation to SO on small metal-containing nanoparticles₃And SO₃With SO₂Compared with the adsorption capacity. These weakly adsorbed sulfur species are also more easily removed during regeneration. This is illustrated, for example, in fig. 6b, where nanoparticles prepared according to the present invention (black lines) show a larger CH than nanoparticles prepared by other methods (black lines)₄And (4) conversion rate. The increase at about 110 minutes shows regeneration, again reaching a higher% conversion than the comparative example. The high% conversion remains at the peak temperature of 550 ℃. By way of further example, the catalysts of the invention also show good water resistance properties. Even after high temperature aging, high performance is maintained compared to catalysts prepared using other types of transition metal precursors. See, e.g., FIG. 6a, wherein the material of the present invention is protectedHigh CH₄The conversion is significantly longer than in the comparative example, even when the temperature is reduced (see the last part of the graph, from about 75 to 100 minutes).

Method of producing a composite material

Generally, the first stage of the inventive process involves providing a suitable amount of a certain type of metal ion-containing compound, wherein the transition metal ions of these compounds combine to form transition metal-containing nanoparticles.

Compounds containing Metal ions-general scheme

It is believed that metal-containing nanoparticles having particularly small particle sizes and uniform distributions can be prepared from metal ion-containing compounds that can form stacks or chains in which the metal ions are arranged. These stacks or chains can have variable lengths. Suitable metal ion-containing compounds are typically (but not exclusively) those having d⁸A configurational complex. Suitable compounds generally adopt a square planar configuration. This is schematically represented, for example, in fig. 2, by way of non-limiting example, using a glyoxime derivative. The figure shows theoretically that the molecules themselves can be positioned such that the metal ions M are relatively close to each other and form a chain-like arrangement. Thus, when several metal ions are present as used in the present invention, it is believed that these types of molecules can form an intimate blend.

Complexes capable of forming such "chain" arrangements have been described in the literature, see for example Day (Chimica Acta Reviews,1969,81), Thomas and Underhill (chem. soc. rev.1, 991972); kamata et al (mol.cryst.liq.cryst.,1995,267,117).

These references describe that two main types of compounds can form such arrangements. These are metal glyoxime, metal salicylaldimine and derivatives of each of these. These types of compounds are expected to be particularly useful in the present invention. Each of these types of compounds can be used as bidentate ligands. The glyoxime-based ligand can coordinate to the central metal atom through two N atoms, and the salicylaldimine-based ligand can coordinate to the central metal atom through one N atom and one O atom.

Without being bound by theory, it is believed that the ability of these types of compounds to form a chain-like arrangement with closely positioned metal ions is important in the present invention. In particular, it is believed that when two metal ions are present, these types of compounds can stack such that the different types of metal ions are intimately mixed. See, e.g., FIG. 2, where M¹Denotes a first metal atom, M²Represents a second metal atom, and M³Represents a third metal atom. [ R represents H or an alternative derivative group, as discussed further below.]Figure 2a shows the situation where two metal ions are present, i.e. it is expected that a bimetallic alloy or a mixture of two metals will result. Fig. 2b shows a situation in which three mutually different types of metal ions are present, i.e. a trimetallic alloy or a mixture of three metals is expected to result. Of course, alloys or mixtures should be produced even if such alternation of metal ions is not a precise uniform alternation as shown in fig. 2. Thus, fig. 2 is representative and not limiting herein, and in practice, a degree of randomization in the metal ion sequence would not be unexpected. Furthermore, it has been described (e.g., Day and Thomas mentioned above) that in some cases, the glyoxime portion of a molecule can rotate about the axis of the metal ion chain as compared to the adjacent molecule in a solid crystal. Fig. 2 is not intended to exclude such rotation.

The metal glyoxime, the metal salicylaldimine and their corresponding derivatives will now be described in more detail.

Metal glyoxime and derivatives thereof

The metal glyoxime-based compound contains a metal atom and an appropriate number of glyoxime or glyoxime derivatives around the metal atom. In the present invention, the metal is a transition metal, and there are (usually two) glyoxime or glyoxime derivatives surrounding the transition metal ion. Such compounds typically form a substantially square planar arrangement.

The present invention preferably employs metal glyoxime or a metal glyoxime derivative as the metal ion-containing compound, and most preferably employs a metal glyoxime derivative.

Glyoxime has the formula C₂H₄N₂O₂. It has the following structure (only one conformation is shown):

the two N atoms of each glyoxime molecule are typically coordinated to the central metal ion in the resulting complex.

As used herein, a glyoxime derivative is a glyoxime in which at least one hydrogen of two C-H groups is substituted by an optionally substituted R group. Thus, glyoxime derivatives can be described by the formula (HO) N ═ C (R1) -C (R2) ═ N (oh).

In the present invention, each of R1 and R2 is independently H, hydroxy, alkoxy, carboxy, or an optionally substituted alkyl, aryl, or heteroaryl group. Thus, when each of R1 and R2 is H, glyoxime is produced. When one of R1 and R2 is not H, a glyoxime derivative is produced.

Preferably, R1 ═ R2, i.e. preferably glyoxime or derivatives thereof, are symmetrical. In some preferred embodiments, R1 and R2 are not both H.

Thus, the glyoxime derivative may have-ROH, -R' COOH or an optionally substituted alkyl, optionally substituted aryl or optionally substituted heteroaryl substituent to replace at least one, and preferably two, of the hydrogens attached to the carbon backbone of the glyoxime molecule. The expression "optionally substituted alkyl, aryl or heteroaryl" means that each of the alkyl, aryl or heteroaryl groups may be optionally substituted. The group R' represents a single bond or an alkyl group as defined below.

Preferably, the glyoxime derivative has an optionally substituted alkyl, aryl or heteroaryl group.

When R1 and/or R2 is an alkyl group, the alkyl group can be linear, branched, or cyclic. Cyclic alkyl encompasses the case where R1 and/or R2 are independently cyclic alkyl groups and where R1 and R2 are linked to each other to form cyclic alkyl.

The linear or branched alkyl group may be a C1-10 alkyl group, preferably C_1-7Alkyl, and more preferably C_1-3An alkyl group. In certain preferred embodiments, R1 and/or R2 is C₁Alkyl (i.e., methyl).

The cyclic alkyl (also referred to as cycloalkyl) may be C3-10 cycloalkyl, preferably C5-7 cycloalkyl, and more preferably C₆A cycloalkyl group.

In a most preferred embodiment, R1 ═ R2 ═ C1 alkyl.

When R1 and/or R2 is aryl, this refers to aromatic hydrocarbons. Suitably, aryl means C₆-9 aryl groups, such as phenyl or naphthyl groups. Particularly preferred are those based on phenyl (C)₆) An aryl group of (a).

When R1 and/or R2 is heteroaryl, this refers to an aromatic hydrocarbon in which one or more, preferably one, of the ring atoms is a nitrogen, oxygen or sulfur group. One of the ring atoms is preferably nitrogen or oxygen, and it is particularly preferably oxygen. Heteroaryl groups typically contain 5 to 7 ring atoms, including heteroatoms. Examples of suitable heteroaryl groups include pyridine, pyrazine, pyrrole, imidazole, pyrazole, oxazole, thiophene and furan. In a preferred embodiment, the heteroaryl group is furan. The heteroatoms may be disposed in any orientation, but are preferably in the alpha position.

Optional substituents of the R1/R2 groups are typically independently-R 'OH, -R' COOH or unsubstituted, linear or branched C1-10 alkyl, C_5-7Aryl or C_5-7A heteroaryl group. R' is as defined above. Preferably, the optional substituent is C1-10 alkyl, and most preferably C1-5 alkyl. Preferably, only one, if any, of the optional substituents is present.

Examples of suitable glyoxime derivatives according to the above are: isopropyl ketoxime, 4-tert-amyl ketoxime, 4-methyl ketoxime, dimethyl glyoxime, ethyl methyl glyoxime, furfuryl-alpha-dioxime, 3-methyl ketoxime, benzil-alpha-dioxime, heptanoxime.

Particularly preferred in the methods described herein is metal dimethyl glyoxime (metal-DMG). Dimethylglyoxime has the following structure:

typically, in a square planar configuration, there are two DMG molecules surrounding each metal center, as described above. For example, when Pt is the central ion and the glyoxime derivative is DMG, platinum bis (dimethylglyoxime) is the metal glyoxime derivative precursor:

different types of glyoxime or derivatives can be used to provide the same metal. For example, the source of Pt can be Pt-DMG₂And Pt-ketoxime₂. Typically, only one type of glyoxime or a derivative thereof is used to provide a single metal. Different types of glyoxime or derivatives thereof can be present in the same complex, for example Pt-DMG-ketoxime, but this is not typical.

In embodiments where more than one metal ion-containing compound is present and where more than one metal ion-containing compound is glyoxime or a derivative thereof, the glyoxime or derivative thereof need not be the same for each different type of metal center. For example, the Pt-containing compound may be Pt-DMG₂And the Ni-containing compound may be Ni-ketoxime₂. However, typically for each metal ion, for example Pt-DMG₂And Ni-DMG₂Only one metal glyoxime or a precursor thereof is provided.

Salicylaldimines and derivatives thereof

The salicylaldimine-based compound comprises a metal atom and a suitable number of salicylaldimine or salicylaldimine derivatives around the metal atom. In the present invention, the metal is a transition metal, and there are two kinds of salicylaldimine or salicylaldimine derivatives surrounding the transition metal ion. Suitable compounds have a substantially square planar arrangement. Notably, salicylaldiminium-containing complexes are sometimes referred to as salicylaldiminium salts or salicylaldiminium salt complexes.

The salicylaldimine has the formula C₇H₅NO. It has the following structure (only one conformation is shown):

each N and O atom of each salicylaldimine molecule is coordinated to the central metal ion in the resulting complex. When coordinated to the metal center, the N atom is generally shown to be positively charged.

As used herein, a metal salicylaldimine derivative refers to a complex of a salicylaldimine derivative having two salicylaldimine derivatives coordinated to a central metal ion through their N and O atoms.

As used herein, salicylaldimine derivatives are salicylaldimines in which the hydrogen of the N-H group is substituted by an optionally substituted group R3, i.e. they are N-methyl derivatives. Thus, salicylaldimine derivatives may be described by the formula (R3) N ═ CH-Ph-OH, wherein Ph represents phenyl and the OH group is located ortho to the (R3) N ═ CH group.

In the present invention, R3 is H, hydroxy, alkoxy, carboxy, or an optionally substituted alkyl, aryl, or heteroaryl group. Thus, when R3 is H, salicylaldimine is produced. When R3 is not H, a salicylaldimine derivative is produced.

Thus, the salicylaldimine derivative may have an-R 'OH, -R' COOH or optionally substituted alkyl, aryl or heteroaryl group to replace H attached to the N atom. The group R' represents a single bond or an alkyl group as defined below.

When R3 is an alkyl group, the alkyl group can be linear, branched, or cyclic.

The linear or branched alkyl group may be C_1-10Alkyl, preferably C_1-7Alkyl, and more preferably C_1-3An alkyl group. In certain embodiments, R₃Is a C1 alkyl group (i.e., methyl).

The cyclic alkyl (also known as cycloalkyl) group may be C_3-10Cycloalkyl, preferably C_5-7Cycloalkyl, and more preferably C₆A cycloalkyl group.

When R3 is aryl, this refers to aromatic hydrocarbons. Suitably, aryl means C₆-9 aryl radicals, such as the phenyl or naphthyl radical, preferably based on phenyl (C)₆) An aryl group of (a).

When R3 is heteroaryl, this refers to an aromatic hydrocarbon in which one or more, preferably one, of the ring atoms is a nitrogen, oxygen or sulfur group. One of the ring atoms is preferably nitrogen or oxygen, and it is particularly preferably oxygen. Heteroaryl groups typically contain 5 to 7 ring atoms, including heteroatoms. Examples of suitable heteroaryl groups include pyridine, pyrazine, pyrrole, imidazole, pyrazole, oxazole, thiophene and furan. In a preferred embodiment, the heteroaryl group is furan. The heteroatoms may be disposed in any orientation, but are preferably in the alpha position.

Optional substituents of the group R3 are typically-R 'OH, -R' COOH or unsubstituted, linear or branched C_1-10Alkyl radical, C_5-7Aryl or C_5-7A heteroaryl group. R' is as defined above. Preferably, the optional substituent is C_1-10Alkyl, and most preferably C_1-5An alkyl group. Preferably, only one, if any, of the optional substituents is present.

Most preferably, in the salicylaldimine derivative, R3 is an unsubstituted alkyl or aryl group, and most preferably an unsubstituted alkyl group. In a most preferred embodiment, R3 is C₁An alkyl group.

A particularly suitable salicylaldimine derivative according to the above is N-methyl salicylaldimine.

As with the glyoxime based metal ion containing compounds, different types of salicylaldimines or derivatives can be used to provide the same metal. Typically, only one type of salicylaldimine or a derivative thereof is used to provide a single metal.

As with the glyoxime-based metal ion-containing compound in which the more than one metal ion-containing compound is salicylaldimine or a derivative thereof, the salicylaldimine or a derivative thereof does not have to be the same for each different type of metal centre, or does not have to be the same in a single complex. However, typically only one metal salicylaldimine or precursor thereof is provided for each metal ion and a single complex.

Embodiments are also contemplated in which at least one metal is provided by a metal salicylaldimine-based compound and at least one metal is provided by a metal glyoxime-based compound.

Metal core

Suitable metal centers are generally transition metal elements, so long as they can form the complexes explained herein. By "transition metal elements" is meant those elements in groups 3 to 12 of the periodic table of the elements and includes Platinum Group Metals (PGMs). Typically, the metal ion-containing compound will include one or more metals selected from the group consisting of Pt, Pd, Mn, Fe, Ni, Ir, Ru, Rh, Co, Cu, Ag and Au. Preferably, the metal centers include those selected from the group consisting of Pt, Pd, Ni, Fe, Mn and Co, with Pt, Pd and Ni being particularly preferred.

Suitably, for the catalytic applications described herein, one of the metal centres of the compound providing the metal ion is Pd. Especially preferred for the catalytic applications described herein are metal ion-containing compounds comprising Pd and/or Pt. For example, nanoparticles comprising Pt and Pd (e.g., in a weight ratio of 20:1 to 1:20, including 1:1) can be prepared by the methods of the invention.

The metal ions of the metal glyoxime or salicylaldimine or derivatives thereof constitute the metal in the nanoparticles described herein. Thus, if a single metal nanoparticle is desired, a metal ion-containing compound having one metal ion should be provided; if a bimetallic alloy is desired, a metal ion-containing compound having two metal ions should be provided; if a trimetallic alloy is desired, a metal ion-containing compound having three metal ions should be provided, and so on. If a single metal nanoparticle is desired, a metal ion-containing compound having one metal ion should be provided.

Provision of metal ion-containing compounds

The metal ion-containing compound can be purchased directly. Alternatively, they may be synthesized from precursors using methods known to the skilled person.

By way of example, for glyoxime or a derivative thereof, synthesis from a precursor typically involves mixing a glyoxime-based ligand such as Dimethylglyoxime (DMG) with a metal salt and forming a solution, typically an aqueous solution. Resulting in precipitation of the metal glyoxime or the derivative thereof.

Typically, a metal to ligand ratio of about 1:2 is used. The range may be between 1:10 to 1:2, such as 1:5 to 1: 2. For cost reasons, a higher proportion of metal is less preferred.

For example, to prepare platinum bis (dimethylglyoxime), an exemplary method is as follows:

the precipitated metal glyoxime or derivative thereof can be purified (i.e., separated from the other components of the solution) in a suitable manner, for example, by filtration and/or washing and/or drying. The skilled person will be aware of suitable purification steps.

In some preferred embodiments, the glyoxime-containing solution can be stirred and/or heated before and/or during the formation of the precipitate. In some preferred embodiments, the heating is performed after the stirring.

Suitable periods of stirring and/or heating will depend on the amount and type of glyoxime-containing solution, but may be, for example, up to 4 hours, up to 3 hours, up to 1 hour, or up to 30 minutes.

Suitable heating temperatures will be known to the skilled person and may include, for example, up to 80 ℃, up to 60 ℃ or up to 40 ℃.

Suitable metal salts will be known to the skilled person, but non-limiting examples may include one or more selected from metal halides, metal nitrates and metal acetates.

In some embodiments, the glyoxime-containing solution is acidified prior to stirring and/or heating it. The skilled person can select from suitable acids, which can be weakly or strongly acidic, depending on the preference. Typically, the acid is an organic acid. Non-limiting examples may include carboxylic acids such as formic acid or acetic acid.

In a preferred embodiment, the composite material of the present invention is prepared by using a precipitation deposition process. Broadly speaking, a suitable amount of a metal ion-containing compound is dissolved in a generally basic solution in the presence of a support. They are precipitated on the carrier with the appropriate amount of acid. Without being bound by theory, it is believed that the rigid ligand backbone of the compounds described herein contributes to the stability (e.g., low instability) of the complex over a range of pH values. The precipitation was found to be approximately quantitative, i.e. most of the metal added as complex was found to precipitate. The process provides good distribution of nanoparticles throughout the support (if present), good catalyst activity and stability, and can be used with a wide range of supports.

Thus, preferably in the methods described herein, a powder of one or more metal ion-containing compounds can be added to a solvent to form a solution comprising dissolved metal ion-containing compounds. Where more than one type of metal ion-containing compound is used, they may be provided as separate solutions (and if desired, different solvents used), so that the separate solutions are mixed later, or they may be dissolved together in a single solution. Suitable solvents include water (and aqueous solutions) and polar organic solvents. As examples of suitable polar organic solvents, DMF and DMSO are mentioned, but the invention is not limited thereto. Mixtures of suitable solvents may be used. Preferably, the solvent is aqueous. The formation of an aqueous solution may be advantageous from a safety and manufacturing point of view.

In some preferred embodiments, the metal ion-containing compound (particularly metal glyoxime or a derivative thereof) can be dissolved by adding a base to form an aqueous solution. Suitably, the solution comprising the metal ion-containing compound is basic. The pH is preferably greater than 8, for example 9. Suitable bases will be known to the skilled person, but include, for example, ammonium derivatives such as ammonium hydroxide and tetraethylammonium hydroxide, or sodium hydroxide and potassium hydroxide.

In a general manner, a solution of the metal ion-containing compound prepared as described above may be mixed with the carrier. The carrier may be present in another compatible liquid if desired. Thus, it may suitably be a suspension or dispersion in a liquid. Thus, the further liquid is preferably polar, most preferably aqueous. It is desirable that the aqueous or polar liquid aids in the dissolution of the metal ion-containing compound.

Usually, an appropriate amount of the metal ion-containing compound is dropped to the carrier, but in some cases, it may be carried out by a single addition or multiple additions. The mixing of the metal ion-containing compound with the carrier can be carried out over a suitable period of time. In general, the suitable time for adding the metal ion-containing compound to the support will be determined by the skilled person, but conveniently will be at most one hour, such as 45 minutes or 30 minutes.

The metal ion-containing compound is suitably mixed with the support prior to the heating step. Suitable methods are known to those skilled in the art, but for example, an appropriate amount of each desired metal ion-containing compound, preferably a mixture of metal glyoxime or a derivative thereof, can be mixed with the support to form a mixture of metal ion-containing compounds.

After addition of the metal ion-containing compound to the liquid, stirring is generally carried out to thoroughly dissolve and mix the components and/or to homogenize the dispersion. Stirring may be carried out for more than 1 hour, such as 4 hours or 8 hours or more. Conveniently, the mixture may be stirred overnight, for example for about 12 hours. Without being bound by theory, it is believed that this step allows for intimate mixing and close proximity of the metal ions. It may also help the metal-containing nanoclusters/nanoparticles to be highly dispersed throughout the support.

Various alternative routes of combining the support with the metal ion containing compound are envisaged, such as preparing the dissolved compounds, mixing together if more than one compound is present, then adding the support, or adding the dissolved compounds to the support separately or simultaneously (usually followed by further stirring). A preferred option is to provide the support in a liquid and add the metal ion containing compound to the support.

The mixing of the support and the one or more metal ion-containing compounds can be carried out under stirring. Once the metal ion-containing compound and the support are mixed, the mixture is typically stirred well to mix as described above. Carriers are preferably used in the preparation methods described herein because they produce supported nanoparticles with improved properties for the present application, such as ease of handling and processing.

Generally, the type of carrier that can be used in the present invention is not particularly limited. Non-carbon based supports such as oxide, zeolite and zeolite based supports are preferred. Suitable oxides include aluminum oxide (alumina), cerium oxide, zirconium oxide, silicon oxide (silica) and titanium oxide (titania) or mixtures thereof. For example, preferred non-carbon based support materials include Al₂O₃、Ce-ZrO_x、SiO₂And TiO₂One or more of (a). Most preferred are ceria and zeolite/zeolite based supports.

Zeolite (or zeolite-like) supports encompass natural zeolites and synthetic zeolites. Silicate zeolites having an Al content range defined by the silica to alumina ratio (SAR) are also contemplated. A preferred lower limit of SAR is 5, preferably 8, and most preferably 10 to obtain hydrothermal stability. The upper limit of SAR may be, for example, 100, more preferably 40. Such materials may have ion exchange sites within the crystal structure. Examples of zeolites suitable for use in the present invention include chabazite-based zeolites and Al-lean zeolites as well as zeolite-based supports. The defects of the Al-lean zeolite can be replaced by, for example, H or OH. Examples of zeolite frameworks suitable for use in the present invention are MFI (e.g., ZSM-5) BEA, CHA (e.g., chabazite, SSZ-13, SAPO-34), AEI (e.g., SSZ-39), MOR (mordenite) and FER (ferrierite). It is believed that the metal ion-containing compound is deposited on the surface of the zeolite in the nanoclusters. During the preparation of the material of the present invention, it is believed that the metal is positioned at the ion exchange sites.

Zeolite structures with little or no Al are also contemplated. In these cases, it is believed that the metal ion-containing compound is deposited on the surface of the zeolite in the nanoclusters.

The carrier may be provided in any suitable form, such as particles, powder or needles. The present invention is not particularly limited in this respect. Powders of the carrier are preferred. The powder may include particles of any desired size (such as microns or millimeters) and any desired shape (including but not limited to spherical or spheroidal). The powder may be crystalline or amorphous, as desired.

For certain applications, such as catalytic flow-through honeycomb or wall-flow filters for treating engine exhaust, the support will typically be formed as a washcoat and will therefore preferably have an average particle size and a particle size range that facilitates the desired rheological properties of the washcoat, for example a particle size of about 0.1 to 25 microns and more preferably about 0.5 to 5 microns.

Other less preferred embodiments contemplate the use of carbon-based supports, such as graphite.

After sufficient agitation to mix, the mixture of support and metal ion-containing compound can preferably be neutralized (i.e., brought to a pH of 7) using any suitable acid. Suitable acids include organic and inorganic acids and mixtures thereof. Mention may be made of nitric acid, sulfuric acid and acetic acid, but these are not limitative. Optionally followed by further agitation after neutralization. Also, conveniently, stirring may be carried out overnight, for example for about 12 hours.

The resulting mixture is typically dried at elevated temperatures (e.g., at about 80 ℃ to about 110 ℃) to remove a substantial amount of solvent, such as water, without burning off any components present in the final product. Drying is suitably carried out slowly and conveniently overnight, for example for about 12 hours. Suitably, the drying is carried out in air.

A dried precursor mixture is obtained.

Heating step

The heating step comprises heating a dried precursor mixture comprising one or more mixed metal ion-containing compounds and a support. This step corresponds to an annealing step that provides the catalyst material from the composite material as described elsewhere herein.

Suitably, the heating may be carried out in a furnace. Preferably, the heating is performed in an oxidizing atmosphere. The skilled person will be able to select from a suitable atmosphere. Suitable oxidizing atmospheres include, for example, air and/or oxygen.

For other less preferred embodiments, an inert atmosphere, which may include, for example, one or more of hydrogen, argon, and nitrogen, or a vacuum, is contemplated.

Thus, the heating is suitably carried out at a temperature of at most 1200 ℃, at most 1000 ℃ or at most 900 ℃. In some embodiments, the heating is performed at a minimum temperature of 300 ℃, preferably at least 450 ℃ or 475 ℃. Preferably, the heating temperature is in the range 450 ℃ to 700 ℃, suitably 450 ℃ to 600 ℃, such as about 500 ℃. The skilled person can determine a suitable heating temperature, in particular for alloys, since the temperature range available can be related to the properties of the metal employed.

Generally, higher temperatures may be preferred for preparing metal alloy nanoparticles. In such cases, the temperature is suitably at least 475 ℃.

Suitably, the heating temperature is achieved by slowly increasing the temperature. For example, the heating rate may be up to 10 ℃/minute, up to 5 ℃/minute, and preferably up to 2 ℃/minute, such as about 1.5 ℃/minute. Thus, the temperature slowly increased from room temperature over several hours. The duration of the heating step is not particularly limited.

For example, the duration of the heating step (including the time it takes to reach the desired heating temperature, also referred to herein as the final temperature) may be between about 1 to 15 hours, preferably between about 5 and 12 hours. For example, the heating step may be performed for up to 15 hours, up to 14 hours, or up to 13 hours. The heating step is preferably carried out for at least about 5 hours, such as 6 hours or 7 hours.

In other embodiments, so-called "flash" heating may have the potential utility of achieving the desired temperature, i.e., rapid heating over a short period of time (such as within minutes). For example, the heating step may be performed for up to 1 minute, such as up to 0.8 minute or up to 0.5 minute.

Once the final temperature is reached, the final temperature is suitably maintained for at least about 5 minutes, such as 20 minutes, and optionally longer. The time during which the final temperature can be maintained is not particularly limited, but is suitably less than about 24 hours or less than about 12 hours. Typically, the final temperature is maintained for between about 0.5 to 8 hours, such as between about 0.5 to 3 hours.

Additional steps

After the heating step, the product is typically cooled, for example, to room temperature. Suitably, the cooling is performed in a furnace in which the heating is performed.

Passivation may be performed after the heating step, but this is not common for the applications described herein. Passivation typically occurs at room temperature. Thus, passivation typically occurs after cooling. Typically, passivation occurs under a mixture of inert gas and oxygen (such as air diluted with nitrogen). Conveniently, the passivation may be carried out in the same furnace in which the heating is carried out. Passivation may advantageously prevent further reaction of the nanoparticles.

Optionally, the resulting metal-containing nanoparticles may be subjected to an acid leaching step. Suitable acids and time stamps are known to the skilled person. By way of example only and not limitation, the leaching step may occur for hours, such as up to 36 hours or up to 24 hours, and the acid used may be any common acid, such as hydrochloric acid, sulfuric acid, or nitric acid. Acid leaching may advantageously render the nanoparticles suitable for use in certain applications. Acid leaching of PtNi oxides is specifically contemplated.

As discussed elsewhere herein, the inventors believe that, in certain embodiments, a coating or capping layer comprising primarily N and C and O may form on the surface of the metal alloy nanoparticles during annealing in an inert atmosphere. For some applications, it may be desirable to remove the capping layer from the surface of the metal alloy nanoparticles. Thus, the metal alloy nanoparticles may optionally be further processed to remove any such capping layers. Removal of such a cover layer may be achieved by any suitable method; for example, an oxidizing agent is used.

Preferred embodiments

Preferred embodiments of the present invention relate to composites and materials prepared from transition metal glyoxime derivatives as precursors for transition metal nanoparticles. In these preferred embodiments, the transition metal precursor is applied to the oxygen-containing support using a deposition and precipitation process. The process preferably involves dissolving one or more metal glyoxime derivatives in an aqueous or polar solvent in the presence of the support and acidifying (typically with stirring) to precipitate nanoclusters of the metal glyoxime derivatives on the surface of the support.

Preferably, the composite material prepared using the precipitation and deposition method is subjected to heating at about 450 ℃ to 700 ℃ under oxidizing conditions to partially, substantially or completely remove the glyoxime-based ligand and form metal-containing nanoparticles on the surface of the support.

The material thus prepared has been found to have a particularly small and uniform particle size and distribution on the support. Thus, they are expected to exhibit good functionality in the applications described herein, and have particular utility in exhaust gas treatment.

Examples

Examples of monometallic and bimetallic DMG precursors were prepared using the reported method (J coord. chem,2008,62(15), 2429-.

The examples were prepared by dissolving Pt-DMG and Pd-DMG with base and mixing with alumina. The corresponding amounts of Pd and Pt salts were suspended in 150ml of water and tetraethylammonium hydroxide was added dropwise until the salts were dissolved. The support was added while stirring and stirring was continued for 15 minutes. Thereafter, the pH of the slurry was adjusted with acetic acid until the pH reached 5. The solid was filtered and washed with deionized water to remove organics. The solid was dried and calcined at 500 ℃ for 2 h. The relative proportions of Pt and Pd are shown in the table below. Three different types of alumina-containing supports were used in examples 1, 2 and 3.

Comparative examples were prepared according to the prior art method (inert water immunization: chem. Rev.,1995,95(3), 477-510). Comparative example Using nitrate-based precursor and γ -A1₂O₃As a carrier.

Each sample was annealed at 500 ℃ in an air atmosphere.

The presence or absence of the alloy was confirmed using energy dispersive X-ray diffraction (EDX) and Transmission Electron Microscopy (TEM), and in some cases, X-ray diffraction (XRD).

The results are shown in table 1. The method of the present invention successfully prepares the alloying material, whereas the prior art schemes have not been successfully prepared.

TABLE 1

These results indicate that the present invention is applicable to a range of metal ratios and supports. It has also been shown that metal alloy nanoparticles can be prepared at lower temperatures than prior art methods. This advantageously reduces costs and reduces the resources required to prepare the material (more environmentally friendly).

Figure 3 shows a representative TEM image and particle size distribution for example 1. The average particle size was 4.7nm (δ ═ 1.3). In this embodiment, the nanoparticles may be considered as spheroid particles, the shape of which is dark. These dark spheroids are separated by lighter regions. The nanoparticles are well-spaced, have good uniformity and distribution on the support, and have similar sizes to each other.

Example 4

PtPd was prepared at high metal loadings (20 wt%) on gamma-alumina at a molar ratio of 1:1 by preforming the binary salt on the support using methods similar to those used to prepare examples 1-3. The annealing was carried out at 500 ℃ in air. This sample was used to evaluate the effect of firing on the nanoclusters. The results are shown in FIG. 4.

Figure 4a shows a composite sample, i.e. a sample before firing. The metal-containing nanoclusters may be observed as white spheroids. These are uniformly below 5nm in size. The composition of the nanoclusters was also confirmed to contain both Pt and Pd atoms.

After annealing at 500 ℃ in air, intermetallic phases are formed. The average particle size increased slightly from 2.4nm (before firing) to 4.3nm (after firing) and ranged from 1.9nm (before firing) to 5.5nm (after firing).

Example 5

The composition of example 5 corresponds to the composition of example 3. It was used to evaluate the effect of aging on nanoparticles formed after annealing at 500 ℃ in air.

The results are shown in FIG. 5. Overall, very little aging effect was found. The average particle size was slightly reduced from 5.6nm to 5.1 nm. The particle size decreased from 14.7nm to 9.0 nm. In fig. 5, the light areas show the positions of the nanoparticles, and they are separated by dark areas. It can be seen that the nanoparticles are spherical and relatively uniform in shape, and are well spaced from each other and have a relatively uniform distribution across the surface of the support.

These results are believed to be promising for extending the life of the catalytic material of the present invention.

Example 6

Pd nanoparticles on zeolite (ZSM-5) were prepared and tested for MeOx activity in a manner corresponding to example 1. Methane oxidation was initially tested under a simple gas mixture of methane and oxygen, then in the presence of water, then in SO₂In the presence of (a).

As shown in fig. 6a, the catalyst was found to have high resistance to water, especially compared to a comparative catalyst prepared using a metal nitrate salt.

As shown in FIG. 6b, although the catalyst was treated with 2ppm SO at a temperature near 500 deg.C₂Deactivated, but activity is recoverable, i.e., the catalyst exhibits good regeneration characteristics. This can be seen in the second half of the figure (where SO₂Turned off) is seen.

Example 7 and comparative example 3

3% by weight of Pd-DMG were dispersed in a manner corresponding to example 1. The Pd salt (1.4g) was suspended in 150mL of water and tetraethylammonium hydroxide was added dropwise until the salt dissolved. The support was added while stirring and stirring was continued for 15 minutes. Thereafter, the pH of the slurry was adjusted with acetic acid until the pH reached 5. The solid was filtered and washed with deionized water to remove organics. The solid was dried and calcined at 500 ℃ for 2 h. For the comparative example, 3 wt% palladium nitrate was dispersed with ZSM-5. Palladium nitrate (7.7g, solution of 7.8 wt% Pd) was diluted to have a total volume of 9ml, and the solution was added to a support (19.7g), and the mixture was uniformly mixed. The solid was dried and calcined at 500 ℃ for 2 hours.

These were fired in air at 500 ℃. The results are shown in FIG. 7.

The comparative examples (fig. 7c, 7d) show that the size of the nanoclusters is about 10nm to 15nm (average 12.6, δ 6.9). Pd-DMG samples (fig. 7a, fig. 7b) show significantly smaller nanoclusters (average 7.2, δ 3.6) of about 6-8 nm. These clusters are located on the surface of the zeolite and are apparent as spherical particles in fig. 7 a. The shapes of the nanoparticles in fig. 7c are generally slightly less than those in fig. 7a, with some particles exhibiting comparable angles. Comparison of the two images also shows that the nanoclusters of Pd-DMG are more evenly distributed over the entire support surface than the Pd-N sample, the particles of which show clear aggregation.

Example 8 and comparative example 4

The effect of the calcination process was studied using the deposition method using 3 wt% Pd on a zeolite support. The results are shown in FIG. 8.

FIG. 8a shows that the nanoparticles prepared using Pd-DMG prior to calcination are small and uniformly distributed on the support surface. The average nanocluster size was determined to be about 2 nm.

FIG. 8b shows that after 2 hours of firing at 500 ℃ in air, the metal nanoparticles formed are larger, about 5-7 nm. They remain uniformly distributed and well spaced and can be identified as individual nanoparticles.

The nanoparticles can be viewed as light colored areas separated by dark gray areas. They are relatively uniform in size, exhibit good uniformity and distribution across the support surface, and are well spaced from each other.

Example 9 and comparative example 5

Tests were conducted on palladium nitrate (Pd-N) and Pd-DMG as described above₂The MeOx characteristics of the 3 wt% loading catalysts prepared, in particular their sulfur tolerance and regeneration characteristics. At 450 ℃ and 2ppm SO₂Next, it was found that the catalyst using Pd-DMG as starting material was less deactivated by SO2 than the corresponding catalyst prepared from Pd-N.

Generally, it was found that the catalysts of the invention are less SO-depleted when rapidly regenerated at low temperatures than corresponding catalysts prepared with nitrates₂And (4) inactivating.

Furthermore, it is noteworthy that the corresponding Pd-DMG prepared by physical mixing and wet impregnation methods₂The catalysts prepared by the methods described herein exhibit better sulfur tolerance and regeneration characteristics than catalysts.

Further experiments showed that the catalytic performance of the catalyst of the invention decreased after high temperature aging, but this was not as significant as the decrease after aging of the catalyst prepared using the Pd — N precursor.

A corresponding improvement was also observed for the catalyst with alumina support.

It will be understood by those skilled in the art that the foregoing embodiments have been described by way of example only, and not in any limitative sense, and that changes and modifications may be made without departure from the scope of the invention as defined by the appended claims.

Example 10 and comparative example 6

1.5 wt.% of Pd-DMG₂Dispersed on an AEI zeolite support and tested as PNA material in a manner corresponding to example 1. The Pd salt (0.47g) was suspended in 150mL of water and tetraethylammonium hydroxide was added dropwise until the salt dissolved. The support was added while stirring and stirring was continued for 15 minutes. Thereafter, the pH of the slurry was adjusted with acetic acid until the pH reached 5. The solid was filtered and washed with deionized water to remove organics. The solid was dried and calcined at 500 ℃ for 2 hours and activated at 750 ℃ for 2 hours. For comparative example, the product was prepared by the initial impregnation method as in comparative example 11.5 wt% palladium nitrate prepared on AEI. The solid was dried and calcined at 500 ℃ for 2 hours and activated at 750 ℃ for 2 hours.

As shown in FIG. 9, PdDMG was found₂The material has higher NOx storage performance at 100 ℃ (left side of fig. 9), especially compared to a comparative catalyst prepared using metal nitrate (right side of fig. 9).

Claims (19)

1. A composite material comprising supported nanoclusters including one or more metal ion containing compounds, wherein each metal ion containing compound is a transition metal complex having a ligand coordinated to a transition metal ion, the ligand selected from the group consisting of: glyoxime; glyoxime derivatives; salicylaldimine; and salicylaldimine derivatives; and wherein the nanoclusters are spaced apart across one or more surfaces of the carrier.

2. The composite material according to claim 1, wherein the ligand is glyoxime or a derivative thereof, preferably having the formula (HO) N ═ C (R1) -C (R2) ═ N (oh), wherein R1 and R2 are each independently H, hydroxy, alkoxy, carboxy or optionally substituted alkyl, aryl or heteroaryl groups, or R1 and R2 are linked together to form a cyclic alkyl group.

3. The composite material of any one of claims 1-2, wherein the support comprises at least one of alumina, ceria, zirconia, silica, titania, and zeolite.

4. The composite material according to any one of claims 1 to 3, wherein the one or more metal ion-containing compounds of the nanoclusters comprise one or more transition metal ions selected from the group consisting of Pt, Pd, Mn, Fe, Ni, Co, Ir, Ru, Rh, Cu, Ag, and Au.

5. The composite material of any one of claims 1 to 4, wherein at least one of the metal ion-containing compounds comprises a transition metal ion that is Pd, Ni, or Pt.

6. The composite material according to any one of claims 1 or 3 to 5, wherein the ligand is salicylaldimine or a derivative thereof, preferably having the formula (R3) N ═ CH-Ph-OH, wherein Ph represents phenyl and the OH group is located ortho to the (R3) N ═ CH group, and R3 represents H, hydroxy, alkoxy, carboxy or an optionally substituted alkyl, aryl or heteroaryl group.

7. A material formed from the composite material of any one of claims 1 to 6, wherein the composite material is subjected to a heating step to form metal-containing nanoparticles from the nanoclusters.

8. A catalyst comprising the material of claim 7, optionally wherein the catalyst is selected from the group consisting of: a methane oxidation catalyst; a diesel oxidation catalyst; a compressed natural gas oxidation catalyst; a NOx reduction catalyst; an ammonia oxidation catalyst; and a gasoline three-way catalyst.

9. A passive NOx adsorber comprising the material of claim 7.

10. A method of forming supported metal-containing nanoparticles or oxides thereof, the method comprising:

a. providing one or more transition metal ions by providing one or more metal ion-containing compounds, and providing a support;

b. dissolving the one or more metal ion-containing compounds in a solvent;

c. a step of mixing the carrier with the dissolved one or more metal ion-containing compounds;

d. a heating step wherein the one or more metal ion-containing compounds are subjected to a temperature of at least 300 ℃ to form metal-containing nanoparticles or oxides thereof on the support;

e. a cooling step comprising cooling the product of step d; and optionally

f. Acid leaching;

wherein the one or more metal ion-containing compounds is a transition metal complex having a ligand coordinated to a transition metal ion, the ligand selected from the group consisting of: glyoxime; glyoxime derivatives; salicylaldimine; and salicylaldimine derivatives.

11. A method according to claim 10, comprising providing a metal ion-containing compound to produce nanoparticles of a single metal or oxide thereof on the support.

12. The method of claim 10, comprising providing more than one metal ion-containing compound to form nanoparticles of an alloying metal or oxide thereof or a mixture of metals or oxides thereof on the support.

13. The method of any one of claims 10 to 12, wherein the heating step is performed in an oxidizing atmosphere.

14. The method of claim 13, forming the material of claim 7.

15. Metal-containing nanoparticles or oxides thereof prepared by the method of any one of claims 10 to 14.

16. Use of at least two metal ion containing compounds selected from the group consisting of metal glyoxime, a metal glyoxime derivative, a metal salicylaldimine and a metal salicylaldimine derivative in a method of forming metal nanoparticles comprising at least two transition metals or an oxide thereof.

17. Use of a metal ion-containing compound which is a metal glyoxime, a metal glyoxime derivative, a metal salicylaldimine or a metal salicylaldimine derivative in a method for forming metal-containing nanoparticles or an oxide thereof, which method comprises dissolving the metal ion-containing compound in a solvent.

18. Use according to claim 16 or claim 17 to form metal-containing nanoparticles according to claim 15 or an oxide thereof; or which forms a composite material according to any one of claims 1 to 6; or which forms a material according to any one of claims 7 to 9; or wherein the method is according to any one of claims 10 to 14.

19. Use of the metal-containing nanoparticles or oxides thereof according to claim 15 as a catalyst or in a passive NOx adsorber.

Images